The present invention relates to a video conference system and method, and more particularly, to a system and method for conducting multi-participant video conference without a multipoint conferencing unit.
With the popular development of network systems and dramatically increasing bandwidth, more and more network-based technologies tend to be applied to low-cost applications. Among those, video conference equipment is one of the best examples.
FIG. 1 shows a popular structure of a multipoint conferencing unit. When a video conference is set up, a multipoint controlling unit (MCU) 101 mixes audio/video signals from user ends 102-105 and then redistributes them to the user ends 102-105. However, increases in capacity for more conference participants correspond to increases in the cost of the MCU.
To avoid high setup costs of the MCU, some have proposed the use of a point-to-point network structure, with IP multicast technology attracting the most attention. This technology involves a router that receives packets from senders and then duplicates the packets to addressees. Such technology omits the expensive MCU and relies heavily on network bandwidth and point-to-point technology. However, the router must be set up by ISP providers, and due to low incentive, the technology is not widely used.
Application-Layer-Multicast (ALM) has been proposed as an alternative solution. This technology uses multiple unicasts to simulate a one-to-many broadcast. The broadcaster has to make many copies himself before sending to other addressees. Under this scenario, the transmission bandwidth constitutes a significant bottleneck.
US patent publication 2006/0187860 discloses a multipoint video conference using ALM, particularly a mesh-connected mutual-cast clique responsible for audio mixing and transmission of voice packets. Although no MCU is required, a mutual-cast clique still needs to be established and maintained. This kind of structure is complicated, has no potential for improving the performance of audio/video streams, and is inconvenient for most users.
US patent publication 2007/0036175 discloses a voice conversation system based on point-to-point technology. This prior art merely establishes a multicast tree, which is used by all nodes to transmit packets. However, such structure is not easy to reinstate if some intermediate nodes in the multicast tree fail. Additionally, because the connection between nodes is fixed, the transmission path is unchangeable. Therefore, it is common for some links to bear a heavy transmission burden, while others bear a light load. Due to the imbalance in loading, the capacity of the network is not efficiently utilized.
In sum, the foregoing prior arts either did not provide a mechanism in the audio/video stream to adequately control flow so as to increase the ALM transmission performance, or failed to balance the loading burden of each link.